1. Field of the Invention
The present invention relates to a swim fin, and more particularly, to a swim fin having at least a pair of movable members disposed on the fin blade thereof.
2. Description of the Prior Art
Swim fins substantially increase the surface area of a swimmer's foot thereby to increase force exerted by the foot on the water when swimming. Such fins generally include a foot-packet formation defining a foot-receiving cavity and a fin blade extending longitudinally beyond a user's foot for a substantial length. However, conventional swim fins currently available on the market all posses some kinds of imperfection in their fin blade design that require to be improved.
The swim fin as disclosed in R.O.C. Pat. 348543 includes a foot-packet formation and a fin blade, wherein the fin blade is integrally formed and is connected to the foot-packet formation by an inclination angle. In addition, both the upper and lower surfaces of the fin blade have a plurality of ribs disposed thereon for directing water flow with respect to the blade surface. As illustrated in R.O.C. Pat. 348543, the swim fin uses repulsive force exerted on the fin blade by water flow to create propulsion while the water flow also exerts drags to the same due to the formation of turbulence around the fin blade. Therefore, conventional swim fins generally can not have satisfactory propulsion efficiency.
Moreover, the swim fin as disclosed in R.O.C. Pat. 427172 includes a foot-packet formation and a fin blade, wherein the fin blade have two outward-inclined side rails and a inward-curled trailing edge. The two side rails and the trailing edge along with the bottom of the blade forms a spoon-like structure that can bags water therein to enable the two side rails to expand outwardly for increasing the amount of water pressured by the same and the operating surface thereof during a kicking stroke. In addition, the counter action of the kicking stroke will enable the two side rails to shrink inwardly for reducing resistance. However, the swim fin of R.O.C. Pat. 427172 still can not solve the problem of the drag exerting on the blade by water flow.
In addition, the swim fins as disclosed in R.O.C. Pat. 422117, U.S. Pat. No. 5,746,631 and U.S. Pat. No. 6,050,868 are unconventional paddle-like swim fins. These swim fins each comprises a foot-packet formation and a fin blade, wherein the fin blade further comprises a plurality of recesses incorporated thereon for directing water flow and two stiffening members arranged respectively at two sides of the fin blade. The fin blade is split down the middle, so it forms a left blade half and a right blade half that are symmetric with respect to each other. This special blade shape, when kick under water, creates propulsion by generating a pressure differential above and below the blade, in addition to the repulsive force created by kicking such that the swim fin can have better propulsion efficiency. However, the overall structural integrity of the forgoing swim fin is not strong enough to endure a long-hour and frequent usage that it is easy to deform.
In view of the above description, if a conventional swim fin has a good structural integrity, it will suffer a poor propulsion efficiency. On the other hand, if a conventional swim fin can create a pressure differential in the water flow to achieve satisfactory performance, it will suffer a poor structural integrity. In this regard, an improved swim fin is required.
U.S. Pat. No. 1,607,857 discloses a prior art swim fin that uses ribs to support a webbing to form a fin structure. The ribs are pivotally connected to a swivel plate and can pivot together with the webbing so as to provide the function of swim fin. However, since the webbing is merely supported by the ribs only, therefore, if the ribs of U.S. Pat. No. 1,607,857 are removed, then the webbing will lose its support and cannot provide the function of swim fin anymore.
U.S. Pat. No. 3,422,470 discloses a prior art swim fin 9 that comprises two rectangular flaps 91 formed on the web 92 thereof as shown in FIG. 9. The web 92 is formed with a longitudinal stiffening rib which is extending along a middle line 93 of the swim fin 9. The rectangular flaps 91 are located at two sides of the middle line 93 and are formed by means of U-shaped through slots 94. Since the two rectangular flaps 91 are symmetric and have the same distance between the trailing edge 95 and the flaps 91, the water flows 961, 962, 963 passing through the flaps 91 will be substantially parallel to the middle line 93 or even dispersed out from the middle line 93 as shown in FIG. 9. As a result, the efficiency and propulsion of the prior art swim fin 9 is also dispersed.